1. Technical Field
This invention relates to adhesively bonding at least two members and, more particularly, to joining at least two members with a mixture of an adhesive and non-compressible beads.
2. Discussion
FIGS. 1 through 4 show a method of making a hemmed joint for inner and outer sheet metal door panels. FIG. 1 shows a first member 10, a second member 12, and an amount of adhesive 14 which has been applied to second member 12. In FIG. 2, first member 10 has been placed into proximity with second member 12, and first and second members 10,12 have been squeezed together. The area where first and second members 10,12 overlap defines an adhesive joint 15. Adhesive 14 has spread throughout the area of joint 15. FIG. 2 further shows a hemming die 18 which is pressed downward to bend a portion of second member 12 into overlapping relationship with first member 10. In FIG. 3, a second hemming die 20 is shown completing the hem by further folding down a portion of second member 12 to overlap first member 10, such that a hemmed portion 22 of second member 12 is parallel with the portions of first and second members 10,12 in the area of joint 15. Quite often, adhesive 23 is squeezed out of the area of joint 15 as a result of completion of the hemming operation. This squeezed-out adhesive 23 is unsightly and often requires removal in an additional manufacturing step where aesthetics is important, such as in the making of an automobile door where inner and outer panels are hemmed together.
Following formation of the hemmed joint 15, the first and second members 10,12 tend to elastically relax and xe2x80x9cspring backxe2x80x9d toward their original positions. FIG. 4 shows joint 15 subsequent to this xe2x80x9cspring backxe2x80x9d phenomenon, which tends to create an air-filled gap 26 between adhesive material 14 and first member 10. Air-filled gap 26 results because adhesive 14 has been squeezed out of joint 15 and an insufficient amount remains to fill the void created by the xe2x80x9cspring backxe2x80x9d of first and second members 10,12. This air-filled gap 26 reduces the area of joint 15, resulting in a weakened joint.
The present invention provides a method and apparatus for adhesively joining at least two members in which a plurality of non-compressible beads are mixed with the adhesive, and one of the members is folded into overlapping relationship with the other in a hemming operation. The beads may be added to the adhesive in a preselected substantially uniform concentration. The apparatus for performing this method includes a container for containing a mixture of an adhesive and a plurality of non-compressible beads. An application gun applies this mixture to at least one of the members to be joined. A pump is employed for pumping the bead and adhesive mixture from the container through the application gun onto at least one of the members. A hemmer then hems one member into overlapping relationship with another.
The present invention further provides a metering device having an improved displacement rod which includes a cooling means for cooling the rod and preventing the adhesive fluid from hardening, thus facilitating insertion of the displacement rod into the metering chamber.